In the rolling on a reversing rolling mill, a pass schedule containing various kinds of data, such as the number of passes and the thickness, tension, roll force and the like of each pass, is determined beforehand, and desired products are manufactured according to this pass schedule. In consideration of mechanical restrictions and operating conditions, usually, a pass schedule is determined on the basis of instruction data from a host computer, such as a “Level 3”, by putting table settings and a mathematical formula model, in which a rolling process is expressed by mathematical formulas, to full use.
One of the important elements of this pass schedule is roll force. That is, if the roll force prediction accuracy is low, excessive roll forces are applied in actual rolling and a desired thickness is not obtained although it has been judged during a pass schedule calculation that a material is capable of being rolled, and in the worst case, it becomes impossible to continue rolling.
In general, on a reversing rolling mill, constant roll force control is often carried out particularly for head and tail portions. Constant roll force control is a rolling method that involves controlling a roll gap so that actual roll forces become equal to reference roll forces. Because at this time control based on measured values of a thickness is not carried out, the roll force prediction accuracy has a direct effect on a thickness when constant roll force control is performed.
Also, even when position control is carried out, usually, the roll opening is calculated from predicted roll force values and hence the roll force prediction accuracy remains to be important. If the thickness accuracy is low, scraps are produced from parts, causing a decrease in yield. Also in consideration of this point, improving the roll force prediction accuracy is essential.
In view of these circumstances, various studies have hitherto been carried out and various proposals have been made to improve the roll force prediction accuracy. For example, in Japanese Patent Laid-Open No. 8-243614, the learning of parameters for a roll force prediction formula is performed for each pass, thereby to improve the roll force prediction accuracy. A pass schedule is corrected on the basis of the results of the learning and predicted roll force values are recalculated, thereby to improve the thickness accuracy.
In Japanese Patent Laid-Open No. 2002-282915, it is claimed that the most important factor responsible for impeding rolling is the difference between predicted roll force values and actual roll force values and that the main factor is ascribed to the difference between nominal thicknesses of a base material and actual thicknesses and the difference between the deformation resistance set in a pass schedule and actual deformation resistance. Furthermore, it is claimed that by calculating actual deformation resistance after the finish of one pass and correcting a pass schedule, it is possible to minimize the difference between roll forces set in a pass schedule and actual roll forces.    Patent Document 1: Japanese Patent Laid-Open No. 8-243614    Patent Document 2: Japanese Patent Laid-Open No. 2002-282915